1316 Configuring Class-of-Service• Weighted Random Early Detection (WRED)—Drops packets queued fortransmission selectively based their drop precedence level. For each of fourdrop precedence levels on each WRED-enabled interface queue, you canconfigure the following parameters:– Minimum Threshold: A percentage of the total queue size belowwhich no packets of the selected drop precedence level are dropped.– Maximum Threshold: A percentage of the total queue size abovewhich all packets of the selected drop precedence level are dropped.– Drop Probability: When the queue depth is between the minimumand maximum thresholds, this value provides a scaling factor forincreasing the number of packets of the selected drop precedence levelthat are dropped as the queue depth increases. The drop probabilitysupports configuration in the range of 0 to 10%, and the discretevalues 25%, 50%, and 75%. Values not listed are truncated to the nextlower value in hardware.CoS Queue UsageCoS queue 7 is reserved by the system and is not assignable. It is generallyrecommended that the administrator utilize CoS queues 0 to 3, as CoSqueues 4-6 may be used by the system for other types of system traffic, forexample, routing protocol PDU handling.Default CoS ValuesTable 41-1 shows the global default values for CoS.Table 41-1. CoS Global DefaultsParameter Default ValueTrust Mode 802.1p802.1p CoS value to queue mapping 802.1p CoS Queue0, 3 11, 2 04, 5 26, 7 3
